About five minutes later I heard banging and found her up against the door on a chair turning the light back on. So I took the chair away, turned the light off again and closed the door. She complained a bit but within a couple of minutes all was silent and I assumed she'd gone back to bed.
I went back in around 20 mins later to find the light on and her cuddling a rather unusual bedtime toy:
I can only assume that she used this to stand on to turn the light back on before going to sleep holding it!